Background: Diagnosis of carpal tunnel syndrome is based on clinicalsymptoms, examination findings, and electrodiagnostic studies. Forcarpal tunnel syndrome, the most useful of these are nerve conductionstudies. However, nerve conduction studie can result in ambiguous orfalse-negative results, particularly for mild carpal tunnel syndrome.Increasing the number of nerve conduction studie tests improvesaccuracy but also increases time, cost, and discomfort. To improveaccuracy without additional testing, the terminal latency index andresidual latency are additional calculations that can be performedusing the minimum number of tests. Recently, the median sensoryulnarmotor latency difference was devised as another way to improvediagnostic accuracy for mild carpal tunnel syndrome.Aims: The median sensory-ulnar motor latency difference, terminallatency index, and residual latency were compared for diagnosticaccuracy according to severity of carpal tunnel syndrome.Study Design: Diagnostic accuracy study.Methods: A total of 657 subjects were retrospectively enrolled. Thecarpal tunnel syndrome group consisted of 546 subjects with carpaltunnel syndrome according to nerve conduction studie (all severities).The control group consisted of 121 subjects with no hand symptomsand normal nerve conduction studie. All statistical analyses wereperformed using SAS v9.4. Means were compared using one-wayANOVA with the Bonferroni adjustment. Sensitivity, specificity,positive predictive value, and negative predictive value werecompared, including receiver operating characteristic curve analysis.Results: For mild carpal tunnel syndrome, the median sensory-ulnarmotor latency difference showed higher specificity and positivepredictive value rates (0.967 and 0.957, respectively) than terminallatency index (0.603 and 0.769, respectively) and residual latency(0.818 and 0.858, respectively). The area under the receiver operatingcharacteristic was highest for the median sensory-ulnar motor latencydifference (0.889), followed by the residual latency (0.829), and lastlythe terminal latency index (0.762). Differences were statisticallysignificant (median sensory-ulnar motor latency difference being themost accurate). For moderate carpal tunnel syndrome, sensitivity andspecificity rates of residual latency (0.989 and 1.000) and terminallatency index (0.983 and 0.975) were higher than those for mediansensory-ulnar motor latency difference (0.866 and 0.958). Differencesin area under the receiver operating characteristic curve were notsignificantly significant, but median sensory-ulnar motor latencydifference sensitivity was lower. For severe carpal tunnel syndrome,residual latency yielded 1.000 sensitivity, specificity, positivepredictive value, negative predictive value and area beneath thereceiver operating characteristic curve. Differences in area under thereceiver operating characteristic curve were not significantly different.Conclusion: The median sensory-ulnar motor latency differenceis the best calculated parameter for diagnosing mild carpal tunnelsyndrome. It requires only a simple calculation and no additionaltesting. Residual latency and the terminal latency index are also usefulin diagnosing mild to moderate carpal tunnel syndrome.